This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Long before modern astronomy, humans looked to the stars and were astounded by what they saw. Even by the most ancient reckoning, the night sky offered enough to inspire awe and wonder, make us feel insignificant, fire our imaginations and foster hope and a sense of connection.
Yet, for as long as humans have surveyed the heavens, they have seen no indication that life as we know it exists elsewhere—what has come to be known as the "Great Silence." For many, the disparity between the assumed prevalence of life in the universe and the lack of evidence for it raises a troubling incongruity often erroneously referred to as "Fermi's paradox" (in truth, it was neither Fermi's nor a paradox). It seems like a valid question when you consider the facts. Given the age, size and density of the known universe, shouldn't we have found unambiguous evidence of extraterrestrial life (and intelligence) by now?
Sixty years after the first search for extraterrestrial intelligence (SETI) experiment (Project Ozma), scientists are still asking the question: "Are we alone in the universe?" In addition to listening to the cosmos for radio signals and other signs of technological activity ("technosignatures"), efforts have been mounted to send messages to space for the purpose of making contact with an extraterrestrial intelligence (ETI). This practice has come to be known as messaging extraterrestrial intelligence (METI) to distinguish it from its more "passive" SETI cousin. Previously, we chronicled the history of SETI by examining some of its greatest milestones.
Today, we will begin looking at the brief(-ish) history of METI and how it came to be. As Universe Today's own Paul Patton addressed, Fermi's paradox is named for Italian American physicist Enrico Fermi. In 1950, during a lunchtime conversation at the Los Alamos National Laboratory, where he had worked a few years prior on the Manhattan Project, Fermi and his colleagues were discussing the recent spate of UFO sightings.
It was here that Fermi posed his big challenge, saying out of the blue: "Where is everybody?" After some quick calculations, Fermi and his colleagues concluded that, if interstellar travel were feasible and desirable, Earth should have been visited several times already. This led to the Hart-Tipler conjecture, named after physicists Michael Hart and Frank Tipler. In a series of papers that appeared between 1975 and 1982, they argued that this "paradox" can be resolved only by asserting that extraterrestrial life does not exist.
Since then, many scientists (including Carl Sagan) have challenged this logic, arguing that there are innumerable reasons why humans have not heard from intelligent life yet (yet being the key word). Or as Sagan and William Newman famously put it: "The absence of evidence is not evidence of absence." From this, the modern definition of the Fermi paradox emerged. It states that the disparity between the assumed prevalence of life in the universe and the lack of evidence for it can be resolved by one of two postulates: either extraterrestrials do not exist, or special circumstances exist that prevent us from detecting them.
Extract — continue reading at the source.
